My translation was: "That is the bear of my aunt." This was marked incorrect, and instead, the following correct answer was given: "That is the bear of my aunt's.". I believe, that the given answer is incorrect. Either, one uses "bear OF my AUNT", or if one want's to use aunt with apastrophe -s, then it should be "my AUNT'S bear". Hence, the translation "that is the bear of my aunt" should be marked correct. Don't you think?
No. Although the meaning is similar, your suggestion would be a different sentence in Czech.
In the DL sentence, "that" is a demonstrative pronoun, whereas in your suggestion, "that" is a demonstrative adjective.
In Czech, the demonstrative adjective ten/ta/to declines according to case and the gender of the following noun. In contrast, the demonstrative pronoun "to" (used in the DL sentence here) does not decline.
The Czech word "to" is used both for the neuter form of the adjective, and also for the indeclinable pronoun. That causes some confusion for English-speaking learners!
Using "that" as an adjective, the Czech would be "ten medvěd je ..." instead of "to je medvěd ...".
That's a brilliantly clear explanation of the (apparently) omnipresent "to" and its relationship to the demonstrative version - thank you. And also great to see the aunt's/aunts' examples in Czech next to each other in your comment above here - also really useful for clarification.